This invention relates to a substrate for producing a gallium nitride compound-semiconductor device and the structure of a light emitting diode.
There has been conventionally investigated process for growing a layer of gallium nitride compound-semiconductor(Al.sub.x Ga.sub.1-x N; X=0 inclusive) in vapor phase on a sapphire substrate using metalorganic vapor phase epitaxy (hereinafter referred to as MOVPE) and also a light emitting diode using the layer of gallium nitride compound-semiconductor as a light emitting layer.
Because a single crystal wafer of gallium nitride compound-semiconductor cannot be readily obtained, gallium nitride compound-semiconductor is epitaxially grown on the sapphire substrate having a lattice constant close to that of the gallium nitride compound-semiconductor.
There has been a problem that a high-quality gallium nitride compound-semiconductor crystal has not been obtained due to lattice mismatching between sapphire and gallium nitride compound-semiconductor as a light emitting layer and to the vast difference in vapor pressure between gallium and nitrogen. Therefore, the light emitting diode proposing highly efficient blue light emission has not yet been obtained.
A process for growing gallium nitride compound-semiconductor on a sapphire substrate is disclosed by one of the inventors of the present invention in U.S. Pat. No. 4,855,249.